Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general to knowledge in the field.
There are various well known and conventional methods for repairing pipes, in particular underground pipes. The most labour intensive is of course a complete replacement or repair of the pipe's concrete/cement lining.
In recent years, new mechanisms have developed for providing a plastic internal liner for the damaged pipe. This permits the damaged pipe to remain in place during and after repair, limits excavation and provides a rapid and relatively inexpensive repair.
One particular technique, and which is subject of several Australian and overseas patents, involves lining a damaged pipe with a helically wound pipe formed from a extruded plastic web (sometimes referred to as a “profile”) with interlocking edges. In one such form, the pipe liner is installed as shown in FIG. 1. A winding machine 10 is lowered into the maintenance hole 20 and positioned at its base. A spool 40 of the profile 50 is provided at the surface. The profile 50 is fed to the winding machine 10 where it is helically wound into the pipe 30 in a reduced diameter form. Generally, to rehabilitate a wastewater main with an internal diameter of 150 mm, a liner with an external diameter of 130 mm is used. This allows the pipe to be installed with minimal friction from one maintenance hole to the next, typically a distance of 50 to 100 metres.
As the profile 50 is wound into the pipe 30, the edges of the profile 50 are interconnected to form the liner 60, but held such that relative movement between the adjacent edges of the respective profiles are prevented until the liner 60 can be expanded to its final position. To explain, the liner 60 is initially inserted into the pipe 30 in a tightly wound form to permit easy ingress of the liner 60 into the pipe 30. As the spool 40 of the profile 50 is unwound, the resultant liner 60 continues to progress along the pipe until it reaches the end of the pipe at the next maintenance hole. At this point the end of the liner 60 is held or fixed. The liner 60 is then expanded as discussed below such that its outer surface contacts the inner surface of the pipe 30, thereby lining and sealing the pipe 30.
In a currently available embodiment shown in FIG. 2, the adjacent edges of the respective profiles which produce the spirally wound liner are held together by locking members 70, 80. The locking members 70 and 80 are provided by ribs 71, 81 on one respective profile, and channels 72, 82 on the directly adjacent profile to accept ribs 71, 81 and thereby hold the wound profile in a spiral configuration. A wire 90 is positioned between the locking members. This wire is then removed from the liner 60 by pulling it radially inward through an opening 91 between the profiles to thereby sever one of the connecting members 70 (sometimes called a to “sacrificial lock”) and permit relative movement between the adjacent profiles and expansion of the liner to the final increased diameter.
Preferably, the sacrificial lock 70 includes an adhesive to hold the liner, and primary lock 80 includes a lubricant to allow relative movement between the adjacent edges of the profile upon severing of the sacrificial lock 70.
A problem may arise, however, in that the longitudinal or axial length of the liner 60 will reduce as the diameter is increased. To explain, as shown in FIGS. 3A and 3B, upon release and radial expansion, the liner 60 will go from helix angle α to helix angle β upon expansion. This change in angle brings the profile closer to a right angle to the longitudinal axis. In turn this will necessarily reduce the length of the pipe from A to B. This reduction in length, sometimes referred to as “creep”, may be of sufficient strength to force the winding machine 10 in direction 150 i.e. towards the pipe being repaired, potentially to contact the pipe or face 100 of the maintenance hole. If sufficient clearance is not allowed between the winding machine 10 and the face 100 of the maintenance hole 20, it is possible that this creep force 150 will cause the winding machine to come into contact with the wall of the maintenance hole and, since at this point further movement is not possible, the interlocking edges of the profile may separate and the liner 60 may fail. This will result in the liner 60 having to be completely removed from the pipe 30. Such a failed liner is of no further use, and cannot be re-installed.
An appropriate clearance between the winding machine 10 and the maintenance hole 20 is difficult to estimate and, usually, it is necessary to remove at least some of the concrete structure in the maintenance hole. This of course requires operator time in the initial installation but also to reinstate the maintenance hole after installation.
The occurrence of creep is quite a complex subject. For each pipe that is spirally wound, as mentioned above, a helix angle is created that is determined by the pitch of the interlocking edges of the profile, the diameter at which the pipe is wound, and the width of the profile used. As the diameter of the pipe is increased upon expansion, for the same profile width, the helix angle comes closer to an right angle to the axis of the pipe and effectively reduces the length of the pipe. During the expansion process, one end of the helically wound pipe liner is fixed and cannot move. The other end of the pipe is in the winding machine and is free to move within the clearance zone created during the initial setup. As the creep force is created during the expansion process, each section of profile needs to move to allow for the new helix angle. In effect, the entire section of the pipe contracts in length.
Another explanation is the small change in lock pitching. Referring again to FIG. 2, when the profile is initially wound, the position of locking member 70 sometimes referred to as a “sacrificial lock”, determines the relative position of the engaging locks 70, 80. When the sacrificial lock 70 is disengaged by the wire 90, a new neutral position is created by the winding forces and the winding tension inside the pipe.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
It is an intention of at least the preferred embodiments of the present application to reduce and preferably eliminate aforementioned “creep” when installing spirally wound expanded pipes.
The term “creep” as used herein refers to force, either tension or compression primarily in the axial direction resulting from radial alteration, eg. expansion or contraction of a spirally wound pipe, pipe liner, or cover.